Ion implantation is an important process in semiconductor/microelectronic manufacturing. The ion implantation process is used in integrated circuit fabrication to introduce dopant impurities into semiconductor wafers. Generally speaking, with respect to semiconductor applications, ion implantation involves the introduction of ions from a dopant species, also commonly referred to as dopant impurities, into a semiconductor substrate material in order to change the substrate material's physical, chemical and/or electrical characteristics. The desired dopant impurities are introduced into semiconductor wafers to form doped regions at a desired depth. The dopant impurities are selected to bond with the semiconductor wafer material to create electrical carriers and thereby alter the electrical conductivity of the semiconductor wafer material. The concentration of dopant impurities introduced determines the electrical conductivity of the doped region. Many impurity regions are necessarily created to form transistor structures, isolation structures and other electronic structures, which collectively function as a semiconductor device.
An ion source is used to generate a well-defined ion beam of ion species from the dopant species. The ion source is a critical component of the ion implantation system, which serves to ionize dopant species that are to be implanted during the implantation process. The dopant ions are generally derived from a source dopant species. The ion-source generates a defined ion beam for a variety of ion species derived from a source dopant gas. The ion source can be a filament or cathode made of tungsten (W) or tungsten alloy. Current is applied to the filament to ionize the source dopant species within an ion implanter. The source dopant species dissociates into corresponding ionic species, which is thereafter implanted into a given substrate.
Current semiconductor device technology utilizes a variety of dopant species. Aluminum (Al) ion implantation is gaining interest in integrated circuit (IC) manufacturing for several applications such as reducing the contact resistance for PMOS devices, tuning work function of metal gates and reducing electro-migration in Cu interconnects. As reported in Kensuke et al. (JVST-A 16(2), 1998) and Rao et al. (Proceedings of 19th International conference on Ion implantation Technology, 2012), AlCl3 is typical dopant source that is utilized for implantation of Al ions. However, process challenges currently exist for effective implantation of Al ions from AlCl3. For example, AlCl3 is a solid under ambient conditions which therefore requires heating to a temperature higher than 200° C. to generate sufficient flux necessary to perform the implant process. Additionally, all of the flow lines from the source gas to the ion source chamber must be heat traced to avoid condensation of AlCl3 therealong. These are examples of the types of challenges in supplying AlCl3 that do not make it a suitable Al implant source gas
As an alternative to aluminum dopant sources which are solids at ambient temperature, Omarjee et al. (U.S. Pat. No. 8,367,531) describes the use of aluminum source compounds which are liquid at ambient temperature. Omarjee et al. presents Trimethylamine-Alane (TMAA), triethylamine-Alane (TEAA), Dimethylethylamine-Alane (DMEAA), mythyl-pyrollidone-Alane (MPA) and trimethylamine-Alane-borohydrate (TMAAB) as suitable Al dopant source compounds. However, the vapor pressure of each of these molecules is unacceptably low such that the molecules cannot be transported to the ion implant chamber without any external heating. TMAA has the highest vapor pressure (2 torr) at the room temperature from the list above. The flow control device requires greater than 10 torr of upstream pressure to maintain the desired flow rate for such processes. In addition, all of the above mentioned molecules contain excessive amounts of carbon in its structure. The use of the above molecules can lead to unacceptable carbon deposition inside the ion source or plasma chamber. Such deposits can interfere with proper functioning of the ion source or plasma chamber and ultimately can lead to their pre-mature failure.
Shibagaki (US Patent Pub. No. 20090190908) suggests the use of Trimethyl-Aluminum (TMA) for Al implantation. TMA is liquid at room temperature and therefore can be conveniently transported to the ion source or plasma chamber of an ion implant system. However, similar to the molecules described in Omarjee et al, TMA is pyrophoric, and hence there is a need to develop a safe packaging and delivery method to handle TMA. In addition, TMA also contains high amount of C in its structure such that excessive carbon deposition in the ion source chamber can cause issues arising therefrom, such as premature of the ion source.
Accordingly, there is an unmet need for an Al containing molecule and associated delivery package that can be used to deliver Al containing gas to the ion implantation system in a safe and convenient manner.